1. Field of the Invention
The present invention relates to a method of and an apparatus for detecting a corrosion degree of a cable made of ferromagnetic materials (e.g., steel) used for, for example, a suspension bridge, a skew bridge.
The term "cable" includes not only a so-called cable made of ferromagnetic materials but also cable-shaped members such as a rope, strand, code, line, wire, thread, string, stick, rod, pole, staff, club, bar, shaft and the like all of which are made of ferromagnetic materials, irrespective of diameters thereof and shapes of the cross section thereof, and further includes a cable comprising line members which are neither twisted nor braided together but just bundled together as well as a twisted cable, throughout the specification and the appended claims.
2. Background Art
A cable made of a metal (particularly, steel) used for a suspension bridge, a skew bridge, and the like is exposed to the weather because it is outdoors. Further, it is affected by salt water in the neighborhood of the seashore, and is affected by sulfurous acid in an industrial area. Therefore, the cable is not immune to corrosion.
The corrosion degree of the cable has been generally evaluated as follows.
With respect to a cable having a diameter of 60 [mm] or less, the damage of the cable has been detected by a magnetic leakage flux testing. In this method, the local damage such as breaking can be detected, but the entire corrosion cannot be evaluated.
With respect to a cable having a diameter exceeding 60 [mm], the appearance of the cable has been viewed, to evaluate the corrosion degree of the cable. In this method, the precision in the evaluation of the corrosion degree of the cable is low.
There is an apparatus for evaluating the corrosion degree of a cable utilizing a so-called total flux method. The apparatus is forced to be increased in size, and its magnetized state varies depending on the measuring environment, whereby the precision may, in some cases, be decreased.